Electronics have been incorporated into many portable devices such as computers, mobile phones, tracking systems, scanners, etc. One drawback to portable devices is the need to include the power supply with the device. Portable devices typically use batteries as power supplies. Batteries must have sufficient capacity to power the device for at least the length of time the device is in use. Sufficient battery capacity can result in a power supply that is quite heavy or large compared to the rest of the device. Accordingly, smaller and lighter batteries (i.e., power supplies) with sufficient energy storage are desired. Other energy storage devices, such as supercapacitors, and energy conversion devices, such as photovoltaics and fuel cells, are alternatives to batteries for use as power supplies in portable electronics and non-portable electrical applications.
Another drawback of conventional batteries is the fact that some are fabricated from potentially toxic materials that may leak and be subject to governmental regulation. Accordingly, it is desired to provide an electrical power source that is safe, solid-state and rechargeable over many charge/discharge life cycles.
One type of an energy-storage device is a solid-state, thin-film battery. Examples of thin-film batteries are described in U.S. Pat. Nos. 5,314,765; 5,338,625; 5,445,126; 5,445,906; 5,512,147; 5,561,004; 5,567,210; 5,569,520; 5,597,660; 5,612,152; 5,654,084; and 5,705,293, each of which is herein incorporated by reference. U.S. Pat. No. 5,338,625 describes a thin-film battery, especially a thin-film microbattery, and a method for making same having application as a backup or first integrated power source for electronic devices. U.S. Pat. No. 5,445,906 describes a method and system for manufacturing a thin-film battery structure formed with the method that utilizes a plurality of deposition stations at which thin battery component films are built up in sequence upon a web-like substrate as the substrate is automatically moved through the stations.
FIG. 1A shows a prior art thin-film battery 20 formed on substrate 22. The battery includes a cathode current collector 32 and an anode current collector 34 formed on the substrate 22. A cathode layer 38 is formed on the cathode current collector 32. An electrolyte layer 42 is formed on the cathode layer 38. An anode layer 44 is formed on the electrolyte layer 42, the substrate 22 and the anode current collector 34. The current collectors 32 and 34 are connected to external circuitry to provide electrical power to the same. In a discharge operation, ions in the anode layer 44 travel through the electrolyte layer 42 and are stored in the cathode layer 38. Thereby, creating current flowing from the anode current collector 34 to the cathode current collector 32. In a charge operation, an external electrical charge is applied to the current collectors 32 and 34. Thereby, ions in the cathode layer 38 are forced to travel through the electrolyte layer 42 and are stored in the anode layer 44.
FIG. 2A shows a prior art method for fabricating the thin-film battery 20. First, the substrate is prepared for deposition of the thin-film battery (step 215). The cathode current collector is deposited on the substrate using DC-magnetron sputtering (step 217). The cathode is deposited on the cathode current collector by RF-magnetron sputtering (step 219). In this method, the magnetron source provides sputtered material having energy of about 1–3 eV, which is insufficient to crystallize the cathode material to form desirable crystal structures that encourage ion movement into and out of the cathode material. The cathode must be annealed to produce a crystalline lattice structure in the cathode, which is necessary to produce an energy-storage device that has the required electrical performance characteristics. In some embodiments, a desired electrical characteristic of a battery is a discharge curve that has a relatively constant voltage (small delta) over a range of capacity and then the voltage decreases rapidly as remaining capacity is exhausted (large delta). Accordingly, the stack of the substrate, cathode current collector and the cathode are annealed at a temperature of 700 degrees Celsius (step 221 of FIG. 2A). The anneal step 221 complicates and adds cost to the fabrication of this type of solid-state battery. Further, the anneal step 221 precludes the use of any material as the substrate or other part of the battery thus formed that is unable to withstand the high anneal temperature. The anode current collector is deposited on the substrate by DC-magnetron sputtering (step 223). The electrolyte layer is deposited by RF-magnetron sputtering (step 225). The anode is deposited by thermal evaporation (step 227).
U.S. Pat. No. 5,597,660 describes a thin-film battery and method for making such a battery. The battery includes an electrolyte amorphous lithium phosphorus oxynitride (LiPON) which is electrochemically stable and does not react with the lithium anode and a vanadium oxide cathode.
One major factor limiting the efficiency of batteries is the internal resistance. A source of internal resistance is resistance created by the electrolyte film, which impedes the movement of ions from one electrode to the other electrode.
Accordingly, there is a need for solid-state energy-storage devices, e.g., thin-film batteries and capacitors, that can be rapidly fabricated and that have acceptable electrical properties for use in a variety of electrical devices. More specifically, there is a need for a fabrication method and system that does not require a high-temperature anneal to form a solid-state energy-storage device.
In the drawings, like numerals describe substantially similar components throughout the several views. Signals and connections may be referred to by the same reference number, and the meaning will be clear from the context of the description.